A disposable absorbent article such as a disposable diaper, bed pad or sanitary napkin comprises an absorbent mat or pad of fluffy, fibrous cellulosic material, enwrapped in wet-strength sheet material through which moisture can pass into the fluffy pad. In the production of all such articles, manufacturing defects occur from time to time that require the scrapping of a certain amount of the product. Because of the complexities of the particular process by which disposable diapers are manufactured, the defect rate tends to be rather high for that product, requiring discard, on average, of about six percent of total production. Although lower, the defect rate for other disposable absorbent products is nevertheless high enough to be economically significant.
The most valuable component of any disposable absorbent product is the fluffy cellulosic material that constitutes its absorbent filler, which costs about $400 per ton to manufacture. Because of the high rate of rejection of disposable diapers and the large amount of fluffy filler contained in each diaper, the recovery of fluff from defectively made diapers is of particular interest from an economic standpoint. From the technological standpoint, the recovery of disposable diaper fluff is somewhat more difficult than recovery of fluff from other disposable absorbent products, and therefore technology that is satisfactory for reclaiming diaper fluff will assuredly be satisfactory for reclaiming fluff from other products. Accordingly, the following discussion will be directed particularly to the recovery of fluff from disposable diapers, not by way of limitation but, on the contrary, by way of an especially significant example.
In the manufacture of disposable diapers, the fluff is caused to adhere to one surface of the sheet that enwraps the filler by means of narrow strips of adhesive coated onto the sheet material. The fluff in a rejected diaper is accessible if the diaper is shredded by means of known machinery, but the fluff that comes out of the shredder is mixed with scraps of plastic, including waterproof backing material, absorbent wet-strength sheet material, elastic strips used in the diaper leg bands, and pieces of the plastic that formed the tie bands. All of these scraps are substantially larger than the individual fluff elements which are very slender fibres about 1/8 inch long.
Heretofore, there has been no technology for separating the fluff from the scraps, and the best that could be done in the interests of conversation was to recycle a small portion of the mixture of fluff and scraps back into the manufacturing process, to be mixed with virgin fluff for the manufacture of new diapers. Obviously the scraps in the mixture comprising the recycled material degraded the entire batch of mixed material, and therefore the amount of recycled material that was used had to be severely limited to avoid reducing diaper quality to an unacceptable level. Accordingly, the greater proportion of the material constituting rejected diapers was simply dumped for land fill.
Such discard of an economically valuable product involves a considerable loss of profits; but it is also regrettable as a loss of valuable forest product, inasmuch as wood is the raw material from which the fluff is produced.
It is evident that any apparatus or process for reclaiming the usable components of defectively manufactured disposable diapers and the like should be relatively inexpensive, since there is no economic gain in recovering the fluffy material unless the total cost of reclamation is no greater than the cost of producing an equivalent amount of new material. As items of reclamation cost, consideration must be given to the amount of capital tied up in the equipment needed for recovery, the cost of the space occupied by such equipment, the costs of labor and energy for operating the equipment, and the percentage of useful material that can be recovered.
It is clear, therefore, that apparatus for the reclamation of disposable diaper filler should be inexpensive and compact, should operate with low energy consumption, and should be as nearly as possible completely automatic. Furthermore, such apparatus should be capable of recovering the highest possible percentage of the desirable material, and the recovered material should be substantially completely free from undesired material.
The problem has existed for a substantially long time, and it has perhaps been obvious during that time that the constituents of shredded disposable diapers could be separated by sifting, inasmuch as the fibre elements of the useful fluff, which are fairly uniform in their dimensions, are much smaller than the scraps of undesired material. What has not been obvious was how an economically worthwhile portion of the fluff could be recovered with an application of the sifting principle. The mixed materials cannot be poured through a sieve or a screen, like sand, because the fluff is so light and clingy that it can be deflected by the lightest breeze and little or none of it will fall of its own weight through the interstices of a screen of suitable mesh. If the mixed materials are entrained in a fast moving air stream that flows through a screen, a little fluff will be pulled through the screen by the air stream, but a substantial amount of the fluff resists passage through the screen because it is entrapped in wads or clumps of scraps that are more or less entangled and tend to adhere to one another and the fluff. Such clumps and wads cannot be broken up by agitation of the screen because the material--especially the fluff--is too light to have any appreciable inertia.
Thus, the separation of fluff from scraps has heretofore been viewed as presenting a technological dilemma. On the one hand, the mixed materials must apparently be subjected to an air stream that flows more or less steadily downwardly through the separating screen, to force the fluff through that screen. On the other hand, such a downward air flow causes the wads and clumps of mixed materials to be confined against the screen and immobilized relative to it, so that such accumulations are not broken up to free the fluff from the entrapping scraps of undesired material. It may have been evident that a turbulent air flow could be employed to tumble and agitate the wads and clumps and thus break them up, but it was not evident how such turbulence could be generated without interfering with the needed downward air flow and without producing upward air flows through the screen that would carry some of the separated fluff back up into the mixed materials.